Spherical porous granules in MgOFe2O3Nb2O5 system: In situ observation of formation behavior using high-temperature confocal laser-scanning microscopy

The pyrolytic reactive granulation process, yielding ceramic spherical porous granules, is simple, consisting of typical ceramic processing methods, viz., wet-ball milling of powders, vacuum drying, granulation via sieving through a screen mesh, and one-step heat treatment for local reactive sintering within each granule. Here, the microstructural development of spherical porous granules was successfully visualized by in situ high-temperature confocal laser-scanning microscopy during the heating up to 1400 °C in air. Based on the result of the in situ observation, a simple but powerful size-controlling process of spherical porous granules, viz., multiscreen sieving after the heating was demonstrated. Nearly monodispersed spherical porous granules composed of pseudobrookite-type MgFeNbO5 were easily obtained.